The present invention is particularly suited for making splices in "medium voltage" power lines. "Medium voltage" as used here refers to its meaning within the usage of electric power utilities to refer to voltage across power lines used for underground transmission and distribution. A nominal range for medium voltage is 2.4 kV to 35 kV. Splicing lengths of underground cable is a necessary function. Customarily, underground electric manholes are provided enclosing a space within which maintenance functions are performed by electrical maintenance workers. The manhole may be a concrete enclosure having a nominal cross section of three feet by four feet in which an electrical maintenance worker can perform various tasks. Routinely maintainable connectors for underground splices are normally housed in an electric manhole.
There are over two million electric manholes in the United States. Generally, the biggest cities have the largest underground power distribution systems. New York City has over 260,000 manholes. It is estimated that there are over 25 million cable connectors in use in the United States. These connectors link customers to power mains in every city's underground transmission system. Many different factors can cause the need to replace a connector. Underground damage due to floods or structural damage may be one reason. Some connectors will need to be replaced out of sheer age. There are connectors in some city systems dating back to the turn of the century.
U.S. Pat. No. 3,689,866 discloses a Heavy Duty Cable Connector which is for connecting cables which may be of different sizes for use in a welding environment, and is for extending the lengths of the cables.
U.S. Pat. No. 3,692,921 discloses a Cable Coupler for joining, branching and terminating high voltage electric power cables intended for use in high rise buildings.
U.S. Pat. No. 3,737,840 discloses a Lug Assembly in which two cables are secured to a bar using a deformable holder which compresses around the cable as it is being placed into a suitable opening in the bar, but a special tool must be used. U.S. Pat. No. 3,740,692 discloses an Underground Distribution Connector Assembly which is a block having a plurality of grooves formed in the block for receiving cables, and a pressure pad associated with each groove which is bolted into place to hold the cables.
U.S. Pat. No. 3,980,374 discloses a Separable Splice Connector in which the cables are connected to lugs with holes which are bolted together.
U.S. Pat. No. 4,415,217 discloses a Cable Joining Connector and Method which is a re-enterable cable jointing connector for cable connection and isolation. It has a system of blades which are inserted into sockets and adjacent blades have holes through which bolts are connected to hold the connection together.
The common forms of splices are: one wire in and one wire out; one wire in and two wires out (or two in and one out) and two wires in and two wires out. The connectors used for these splices are respectively referred to as I, Y and H connectors. The splices formed using these connectors are known as I, Y and H joints. These joints need to be capable of withstanding harsh conditions. These conditions may include submersion in freshwater, saltwater or mud and high ambient temperatures.
The four most common types of splicing methods (methods of connection) are listed below and will be discussed as follows:
1.) lead joints; PA1 2.) pre-molded joints; PA1 3.) heat shrink joints; and PA1 4.) cold shrink joints. PA1 It is not made from lead; PA1 It can be reused; PA1 It can be quickly disconnected; PA1 It is completely boltable requiring no soldering; PA1 It reduces splicing time; PA1 It preserves any unused end with a protective end cap; PA1 It will fit a multitude of cable sizes in that there is a means which fits into the bolting port at any angle, which simply wedges into the bolt clamp at the necessary angle to allow for a fit of any size cable ranging from 0.20 inches in diameter to 0.575 inches in diameter and by removing this means the connector will handle larger cables; PA1 The system is designed to properly handle all standard cable types such as paper and lead, as well as, solid dielectric cable types such as aluminum and copper; and PA1 The end caps which are provided have a major use as a jacket for over the connector to be sealed with rubber tape, but a secondary use is to cover an empty connection port. PA1 1.) boltable connector; PA1 2.) spade cover; PA1 3.) wedge; PA1 4.) end cap; and PA1 5.) tie-down bar.
1.) Lead Joints.
A traditional means for splicing, still in use today, is a lead joint. A worker uses a propane torch to solder two cable ends with a lead material. Skilled labor is required to handle hot solder. When such a joint is taken apart, the connector is destroyed. Lead is hazardous to both the environment and to the worker making the connections.
2.) Pre-molded Joints.
Pre-molded connections will handle only some of the more traditional cable types and only cable with solid insulation. They must be molded into the shape needed for the installation. This form of connection is also costly because many different parts are needed for different sized cable. The pre-molded connector joints have a potential safety problem. If a test point cap falls off, a test point may be exposed which may provide a direct contact to the conductor.
3.) Heat Shrink Joints.
The next type of joint is a connection of the cable to the connector and which is covered by heat shrinkable material. A torch is applied to the heat shrinkable material to seal the connection. The torch burns oxygen in the manhole, or trench, in which a worker is performing the connection tasks and may cause oxygen deficiency. Such a connection is difficult to break when adding a tap or removing a tap from the connector.
4.) Cold Shrink Joints.
Cold shrink technology also uses sleeves to cover a connection. Connections require careful cable preparation. This form of connection is also costly.
In past years, when electric utilities were guaranteed a profit, cost cutting was not as critical a concern. However, with the greater scrutiny of rate-making and the prospect of competition, cost-cutting is more heavily emphasized.
More recent innovations in the art have included connector bodies to which lugs are bolted after a power cable is crimped to each lug.
Heat-shrink sleeves must be cut away. They cannot simply be slipped off a connector. Also, a variety of different parts must be inventoried to provide the capability to provide I, Y or H configurations. For both shrink-sleeve and pre-molded connectors, many different parts must be inventoried for making I, Y or H joints. In the present state of the art, there is no "standard" connector and kit with wide versatility providing for simplicity and low cost in use. The trade press has stated that today in the power industry, when it comes to splicing medium voltage, underground distribution cable, "it seems there is no best way; a goof proof splice that fits all cable sizes, under all conditions, and is simple to install would be just the ticket." W. Koch, Electrical World, Vol. 211, April, 1997.